We are applying the unique capabilities of the staphylococcal exfoliatin to the study of normal and neoplastic keratinocyte surface structure. Methods for the preparation of high resolution replicas of these intraepithelial surfaces have been developed, which have revealed the extracellular aspect of the keratinocyte for the first time. Findings include the substructure of the external face of desmosomes, which contains particles in a distribution similar to those seen in freeze-fracture. Labels have been developed for the identification of cholesterol in keratinocyte plasma membranes, and normal keratinocytes lack cholesterol in protein-enriched membrane regions, such as gap junctions, coated vesicles, and desmosomes. Initial studies of neoplastic vs normal cells indicate substantial differences in surface structure and free sterol distribution.